Global positioning systems (GPS) are widely used in mobile vehicles to provide accurate location identification of its location in terms of geographical coordinates. Such systems operate by GPS data transmitted from GPS satellites orbiting the earth and received by a GPS receiver collocated with the mobile vehicle. Data coordinates are transmitted by the satellites and are converted by receiver equipment to geographical coordinates, latitude, longitude and height. The location of the vehicle may be continuously updated as the vehicle moves from one location to another. In some applications GPS has been combined with cellular telephone service so that a stationary monitor may call a moving vehicle and receive the vehicle's geographical coordinates in a return call over a cellular radiotelephone channel.
Cellular digital packet data transmission (CDPD) systems have become commercially available and are used to communicate data to personal communicators and to cellular receivers in mobile vehicles. Such data may be also used to transmit instructions to smart processors in the vehicle or may be used for the transmission and receipt of Faxes. This CDPD data is normally transmitted by cellular voice channels by frequency hopping techniques to avoid interference with voice traffic.
Each of these systems allow communication with mobile vehicles, especially coordinated fleets, to transmit information and to obtain location information about a particular vehicle. Often this information is obtained by voice communication by a dispatcher with a vehicle operator. It may desirable to obtain such information automatically and to automatically provide location pertinent information to the vehicle.